ABSTRACT

Intrinsic nonproportionality is a material dependent phenomenon that
sets an ultimate limit on energy resolution of radiation detectors. In
general, anything that causes light yield to change along the particle
track (e.g., the primary electron track in γ-ray detectors) contributes
to nonproportionality. Most of the physics of nonproportionality lies in
the host-transport and transfer-to-activator term. The main physical
phenomena involved are carrier diffusion, trapping, drift in internal
electric fields, and nonlinear rates of radiative and nonradiative
recombination. Some complexity is added by the now well-established
fact that the electron temperature is changing during important parts of
the physical processes listed above. It has consequences, but is
tractable by application of electron-phonon interaction theory and
first-principles calculation of trap structures checked by experiment.
Determination of coefficients and rate "constants" as functions of
electron temperature Te for diffusion,
D(Te(t)); capture on multiple
radiative and nonradiative centers, A1i(Te(t));
bimolecular exciton
formation, B2(Te(t));
and nonlinear quenching, K2(Te(t)),
K3(Te(t)) in
specific scintillator materials will enable computational prediction of
energy-dependent response from standard rate equations solved in the
electron track for initial excitation distributions calculated by
standard methods such as Geant4. Te(t) itself is a
function of time.
Determination of these parameters can be combined with models describing
carrier transport in scintillators, which is able to build a userr's
toolkit for analyzing any existing and potential scintillators. In the
dissertation, progress in calculating electronic structure of traps &
activators, diffusion coefficients and rate functions, and testing the
model will be described.